The present invention relates to a pinch roller apparatus for feeding a magnetic tape sandwiched between a capstan that is forced to rotate and to a pinch roller apparatus in a video tape recorder (VTR) or the like, and to a pinch roller used in such a pinch roller apparatus. More specifically, the present invention relates to a pinch roller of a structure having a resin bearing press-fitted inside a cylindrical elastic body, and a pinch roller apparatus using such a pinch roller.
A pinch roller is generally fabricated by attaching rubber through baking or the like on the outer circumferential plane of a metal sleeve that has a bearing inside. Also known is a pinch roller of reduced cost having a structure which has a resin sleeve of bearing capability press-fitted through rubber that is molded in a cylindrical configuration. The cost can be reduced since fewer components are used, and attaching rubber to the sleeve is not required.
FIG. 6 shows an example of a conventional pinch roller apparatus disclosed in Japanese Utility Model Laying-Open No. 62-113435. Referring to FIG. 6, the pinch roller apparatus includes an elastic body (rubber portion) 1, a resin sleeve (resin bearing) 2, a roller shaft 5, an arm 6, and thrust bearings 8 and 8a. 
Resin sleeve 2 is press-fitted at the inner diameter side of elastic body 1. A clearance is provided between resin sleeve 2 and thrust bearings 8 and 8a in the direction of the thrust by thrust bearings 8 and 8a. Elastic body 1 and resin sleeve 2 are supported by roller shaft 5. Roller shaft 2 is secured to arm 6.
A pinch roller of a structure in which resin sleeve 2 is press-fitted inside a cylindrical elastic body has the disadvantage that, when elastic body 1 is to be ground after resin sleeve 2 has been press-fitted during the fabrication stage of the pinch roller, sliding will occur between elastic body 1 and resin sleeve 2 since resin sleeve 2 that functions as a plain bearing has a high sliding property. Thus, there is the problem that grinding cannot be easily carried out.
Therefore, it was conventionally necessary to fit the elastic body 1 to a grind-oriented shaft, wherein the outer circumferential plane was ground and then fit to a resin sleeve 2 after the grind-oriented shaft is removed. This extra processing step complicates the fabrication process. Furthermore, the roundness is not improved, resulting in the problem that deflection in rotation becomes more serious.
In a pinch roller apparatus, force is exerted on the outer circumference of elastic body 1 from the capstan shaft. If the holding force of elastic body 1 relative to resin sleeve 2 is small, sliding will occur between elastic body 1 and resin sleeve 2 which results in displacement of the elastic body 1 with respect to resin sleeve 2.
In order to solve the problem of sliding, the holding force of the elastic body 1 relative to resin sleeve 2 should be increased. In other words, the elastic body 1 should be fixed to resin sleeve 2 in a slightly elongated state.
However, if the elongation of elastic body 1 is increased too much, the elastic body 1 will become more susceptible to oxidation. This will facilitate the generation of cracks at the outer circumference of elastic body 1. The presence of such a crack is critical for a pinch roller.
The aforementioned fabrication teaches only the press-fitting of resin sleeve 2 in the inner diameter side of elastic body 1, and provides no disclosure or suggestion of a method of suppressing degradation of elastic body 1 while improving the holding force thereof.
It can be said that the pinch roller apparatus of the aforementioned publication cannot have degradation of elastic body 1 suppressed while preventing slipping between elastic body 1 and resin sleeve 2.
In view of the foregoing, an object of the present invention is to suppress degradation of an elastic body while preventing slipping between the elastic body and a resin sleeve in a pinch roller having the resin sleeve press-fitted in the elastic body.
The pinch roller of the present invention includes a cylindrical elastic body formed of a polymer blend including acrylonitrile-butadiene copolymer rubber and at least one of a highly saturated copolymer rubber containing nitrile group obtained by hydrogenating a butadiene part of acrylonitrile-butadiene copolymer rubber, and ethylene-xcex1-olefin type copolymer rubber, and a resin bearing press-fitted in the elastic body. The elastic body has an elongation of at least 5% and not more than 15%.
The pinch roller apparatus of the present invention includes a cylindrical elastic body formed of a polymer blend including an acrylonitrile-butadiene copolymer rubber and at least one of a highly saturated copolymer rubber containing a nitrile group obtained by hydrogenating a butadiene part of the acrylonitrile-butadiene copolymer rubber, and ethylene-xcex1-olefin type copolymer rubber, and a resin bearing press-fitted in the elastic body, a roller shaft inserted through the resin bearing, and an arm holding the roller shaft. The elongation of the elastic body is at least 5% and not more than 15%.
In the present invention, the elongation of an elastic body is defined as the percentage of the elongated value of the inner diameter of the elastic body before and after the resin bearing (resin sleeve) is press-fitted into the inner diameter of the elastic body.
By setting the elongation of the elastic body in the pinch roller to the range of at least 5% and not more than 15%, the holding force of the elastic body relative to the resin bearing can be ensured. The sliding between the elastic body and the resin bearing can be suppressed as shown in the following Table 1 to Table 3. By virtue of the above specified range, displacement of the elastic body caused by the slide between the elastic body and the resin bearing can be suppressed even in the case where the outer circumferential plane of the elastic body is ground with the elastic body mounted around the resin bearing. If the elongation of the elastic body is lower than 5%, there is a possibility of sliding occurring between the elastic body and the resin bearing when the outer circumferential plane of the elastic body is ground with the elastic body mounted around the resin bearing or during operation of the pinch roller apparatus, as shown in Table 4. As shown in Table 2, Table 3 and Table 5, the oxidation resistance of the elastic body can be ensured by setting the elongation of the elastic body to at least 5% and not more than 15%. If the elongation of the elastic body is larger than 15%, the elastic body is susceptible to degradation caused by oxidation. There is also the possibility of a crack being generated at the outer circumference of the elastic body.
The elastic body is formed of a polymer blend including acrylonitrile-butadiene copolymer rubber and at least one of highly saturated copolymer rubber containing a nitrile group obtained by hydrogenating the butadiene part of acrylonitrile-butadiene copolymer rubber, and ethylene-xcex1-olefin type copolymer rubber.
By virtue of the elastic body including at least one of a highly saturated copolymer rubber containing nitrile group and ethylene-xcex1-olefin type copolymer rubber, oxidation of the elastic body can be suppressed to improve the weather-resistant property, even if the elastic body is fixed to the resin bearing in an elongated state. Since the elastic body additionally includes acrylonitrile-butadiene copolymer rubber, oil resistance can be ensured while improving the weather-resistant property. Especially, the elastic body is preferably formed of a polymer blend including acrylonitrile-butadiene copolymer rubber and an ethylene-xcex1-olefin type copolymer rubber.
The thickness of the elastic body is preferably at least 0.6 mm. Accordingly, the desired holding force of the elastic body can be ensured. Displacement caused by the sliding between the elastic body and the resin bearing can be suppressed effectively. If the thickness of the elastic body is smaller than 0.6 mm, there is a possibility of displacement caused by sliding between the elastic body and the resin bearing. The upper limit of the thickness of the elastic body is preferably, but not limited to 5 mm and below.
The pinch roller of the present invention is for use with a video tape recorder. The length of the elastic body in the axial direction is preferably at least 5 mm and not more than 20 mm. The present invention is applicable to a pinch roller for a video tape recorder having such a length in the axial direction.